Telecine machines are well known. Examples of such machines include the "URSA Diamond" manufactured by Cintel International Limited in Ware, England and the FDL 90 manufactured by Broadcast Television Systems (BTS) in Darmstadt, Germany. The URSA Diamond is the latest in the URSA series of telecines, which represent the most commonly used "flying spot" telecine machines. In a flying spot telecine, a spot of light (the "flying spot") is produced on the face of a cathode ray tube (CRT) by bombarding the phosphor on the inside of the CRT face with a beam of electrons. The beam of electrons is controlled so that the flying spot traces a raster pattern across the face of the CRT. The light from the CRT is directed through a film frame and is detected after it has passed through the film frame by a photodetector. The photodetector produces an electrical signal corresponding to the intensity of the received light. In a colour telecine, photodetectors are provided corresponding to each of the primary colours of light, i.e. red, green and blue, to produce electrical signals corresponding to the detected intensity of each of these components. As the flying spot moves across the face of the CRT, and thus across the film frame, the electric signals from the photodetector(s) are sampled at each position of the spot to build up a set of signals corresponding to the colour transmission of the film frame, and thus the image on the film.
Known flying spot telecine machines use a single phosphor which has a relatively narrow spectral output across the wavelengths of the visible spectrum. The light from the CRTs of such telecines is generally greenish yellow and has little blue or red content. This means that the average level of detected red or blue light transmitted by the film will be lower than the average level of the detected green light, resulting in a low signal-to-noise ratio (SNR) in the red and blue channels.